The use of video conferencing systems as a means of conducting meetings, presentations and other matters continues to gain in popularity. Video conferencing systems generally allow users separated geographically to both see and hear one another. A typical video conferencing system is illustrated in FIG. 1.
Video conferencing system 10 generally includes a local station 12 and a remote station 14. Each of the local and remote stations 12 and 14 includes a video conference processor 16, a camera 18, a monitor 20, a microphone 22 and a speaker 24. Certain of these elements may be combined within a single unit. For example, the housing for monitor 20 may also include the video conference processor 16 as well as the microphone 22 and speaker 24. In such systems, camera 18 may be a separate, stand-alone device or may also be incorporated within the housing of monitor 20. In other embodiments, each of the elements may be stand-alone devices.
Local station 12 and remote station 14 are connected by a transmission medium 26. In some cases, transmission medium 26 may be the Public Switched Telephone Network (PSTN) or, in other cases, transmission medium 26 may be an ISDN line or other transmission medium.
In general, during the video conference, video images captured by camera 18 at local station 12 are filtered and encoded by video conference processor 16 prior to transmission to remote station 14. Similarly, audio signals captured by microphone 22 are filtered and encoded by video conference processor 16 prior to transmission. At remote station 14, video and audio data received from local station 12 are expanded and processed prior to display on monitor 20 and speaker 24. Likewise, video and audio signals captured by camera 18 and microphone 22 at remote station 14 are encoded by video conference processor 16 prior to transmission to local station 12. At local station 12, this video and audio data are expanded prior to display on monitor 20 and speaker 24.
FIG. 2 further illustrates the encoding process performed by video conference processor 16 at local and remote stations 12 and 14. Video signals from camera 18 are passed to video processor 28. Video processor 28 performs filtering operations on the video images, for example, to remove high frequency components such as noise produced by camera 18. Filtered images are passed from video processor 28 to video encoder 30 for compression prior to transmission.
During a video conference, a variety of images may be captured and transmitted by a video conference system. For example, as shown in FIG. 3A, "long shots" in which a relatively wide angle scene is captured as a image may be transmitted between local station 12 and remote station 14 for display. As shown, the resulting image displayed on monitor 20 at remote station 14 may be such that a user at remote station 14 can view a wide angle presentation or group of people, etc. At various times during the video conference, the user may wish to zoom in on aspects of the presenter or the presentation. FIG. 3B illustrates an example where the user has zoomed in on the presenter, for example, during an especially interesting portion of the discussion. To effect this zoom in, the user at remote station 14 transmits zoom commands to the local camera 18 stationed at local station 12. In response, camera 18 zooms in on the presenter at local station 12 so that the resulting image is displayed. At other times during the presentation, the user at remote station 14 may wish to zoom out so that the entire scene is displayed on his monitor 20.
At times when the scene to be captured by camera 18 has a relatively wide angle, certain image details may be unimportant and, hence, need not be transmitted to remote station 14. However, at the same times, motion within the scene, for example gestures by the presenter towards a presentation display, may be important. Accordingly, filtering provided by video processor 28 at local station 12 should be such that accommodates motion within sequential video images but need not be such that a accommodates a great amount of image detail. In contrast, during periods of zoom in, image detail becomes important while motion compensation need not be as important. Thus, at these times video processor 28 should apply filtering to achieve improved image detail.
Typically, video processors such as video processor 28 of video conference processor 16 are incapable of providing different filtering algorithms at different time during a video conference. Accordingly, what is needed is distance adaptive filtering means which achieve optimum performance according to the scene captured by a camera.